Build a house on an old barn/farmyard

You can upload some pictures. What do you mean by "ca. 11 m bis Oberkante Dach" - ridge height or eaves height?

Approximately when is the building from?

Two things are expensive in construction debris disposal: a mix ("not sorted") of stones, wood, iron, plastics, glass; and hazardous substances / special waste (e.g. asbestos) or rotted material.

I suspect a classic Einhaus - is it a Mittertennhaus or a Mitterstallhaus? - in any case, you would have to have a local or at least regionally familiar carpenter with the building type take a look at where possible structural separation points could be (if I understood correctly, you want to cut off and rebuild about 18 m length from a 50 m single-roof / single-ridge house).

And how quickly will the new building be up again? Just approximately, I have no idea at all whether it takes 2 months or a year. What do you think about such a project and the size of a solid wood house? I like it in that regard because there is simply no dirt and the whole thing goes faster? (How fast?)

As I said, I am not the type of person who wants a construction site in front of the door for years, my nerves can't handle that, I am a bit of a perfectionist and everything has to be in order

Then forget that very quickly. As others have already described, the old building must not be structurally damaged during demolition, yet 50,000€ demolition costs seem too high to you. I think that is realistic, however, as has also been advised to you, you should first obtain legal certainty for the new building before you think about demolition.

I think 2-3 hours with a capable architect will open your eyes to what you are planning and whether it is even realistic.

As a perfectionist and order fanatic, you will also have plenty of fun as a landlord in the immediate neighborhood (if I recall correctly). /Irony

Best regards Dirk Grafe

You can upload pictures. What do you mean by "approx. 11 m to the top edge of the roof" – ridge height or eaves height?

Approximately when was the building constructed?

I suspect a classic Einhaus – is it a Mittertennhaus or a Mitterstallhaus? – in any case, you should have a local or at least regionally familiar carpenter with this type of construction take a look where possible structural separation points might be (if I understood correctly, you want to cut off about 18 m from a 50 m single-roof / single-ridge house and rebuild it anew).

Approximately 11 m ridge height
The building is over 300-350 years old
The top floor + roof structure was newly added in 1950 and, comparatively, is "good".

Correct, the building is part of a row. The first 18 meters are to be removed, and then exactly the same thing attached there again.

I like the idea of using Ytong as already mentioned. Can anyone roughly say the cost advantage of a standard brick masonry house compared to a Ytong house? For example, if a shell construction with bricks costs 100,000 and a shell construction with Ytong costs 50,000.
Can someone tell me how the prices compare?

I just find it strange that you never see something like this with Ytong. I’ve seen many construction sites but never one with Ytong.

Ytong is a stone that is not so popular down in your south. The advantage compared to Poroton bricks is that with a reasonable wall thickness of 36.5cm you can meet the energy saving regulation without additional thermal insulation. (With Poroton you probably have to use ones filled with perlite) This of course saves labor costs, as an entire work step is omitted. That is why Ytong is at least popular in the north. The masons also cover area quickly because of the large formats, Ytong is sawn, despite the size of the planar blocks it is not too heavy, spares the masons’ backs, it is processed with a kind of adhesive, so there is little water in the masonry. But... whether 11m ridge height is possible with Ytong, whether there are companies near you that work with it, whether it is worthwhile, you have to check on site. By the way: Ytong contains a lot of air, does not have the best sound insulation. Which probably doesn’t matter in the countryside.

My masonry costs in Ytong with plaster are 28,000 plus tax for 10m by 13.5m by 2.75m. Stone, mortar, plaster and labor. Karsten

By the generic term, that stuff is called "aerated concrete" by the way; besides the other big manufacturer Hebel, there are also smaller ones. Ytong has just become a synonym like Tempo or Tesa.

Aerated concrete is very light – not only easy to lift, but also easy (in the sense of effortless and with simple tools) to saw. The first has led to an era of large-format stones, which significantly speeds up masonry. The second makes this building material popular for use as infill, so it is found quite frequently in timber frame renovation.

Its weight makes it statically less demanding to build interior walls differently than the ones of the underlying floor. As far as I know, it is approved up to eight stories.

It can be manufactured precisely (meaning smooth-edged), therefore it has long been available as a "plan block" with a thinner adhesive layer (like with tiles) instead of a centimeter-thick mortared bed joint. That makes it a stone whose workability for DIYers already comes close to drywall, and consequently popular for kit houses.

Prices (and thus price relations to other products) vary greatly regionally.

Aerated concrete is stable and, as said, easy to fit. That also makes it well suited to replace damaged parts of existing walls. I assume that the construction method of your house will thwart you from "surgically precisely amputating" a lengthwise section of the "row house."

A building material also popular in renovations is sand-lime brick: it does not have to be tied in, but may butt up flush against exterior walls as an interior wall. Therefore, where one has to join masonry interior walls to a timber frame exterior wall to be preserved, sand-lime brick is also gladly used.

Regarding sound insulation, I personally prefer practical experience over theories. My father already lived in aerated concrete, I myself was a tenant in a hall made from that stuff. Unplastered, the surface is even slightly sound-absorbing – though not chic for residential construction. I know sand-lime brick from family friends who had a house made of it as exposed masonry. And from my school days from the gymnasium.

Expanded clay (also here again: Poroton is a brand name) I also find good. In my area, a lot is still built with pumice. Vulkaneifel, after all.